塔克拉玛干沙漠克里雅河下游地区风沙地貌的形成发育与环境变化趋势的初步研究

克里推河是塔里木盆地中深入到塔克拉玛干沙漠内部的主要河流之一。克里稚河出山口后形成的冲积扇, 上部为砾石平原, 中部为亚沙土, 沙壤土的细土平原, 当前农业绿洲所在, 下部为盐土平原, 在野营以下, 河流又分成东西两支, 各形成东西两个干三角洲。在东部干三角洲上, 水系扇状扩散, 沿河两岸呈现胡杨、红柳灌丛的天然绿色植被带, 复合型沙丘链被流水切割, 形成孤立复合型沙丘散布面积约210Km², 居民点零散分布其间。在西部干三角洲上, 扇状水系的干河床断续分布。河床内为密集新月形沙丘和沙丘链, 两侧为吹扬的灌丛沙堆和有枯死的胡杨林地。并有历史上城镇废墟分布, 反映着历史时期曾有过人类活动。克里雅河下游上段(大河沿——于田地段)河漫滩部分受间歇洪水影响, 芦苇丛生, 尚未有沙丘发育。高出河床1.5-3m第一阶地为红柳灌丛和胡杨分布地区, 疏林地段有新月形沙丘、沙丘链和灌丛沙堆。高出河床8-10m第二阶地主要为红柳灌丛分布地区。并受外围流沙入侵影响和固定沙丘"活比"形成新月形沙丘、沙丘链与吹扬灌丛沙堆相间的景观。第三阶地已全为裸露新月形沙丘及沙丘链覆盖。再往外则系高大的复合型沙丘。下游中段(大河沿以北)为克里雅河下游扇状平原干三角洲, 水分条件较好, 成为沙漠中一片绿洲。只有被淤高干河床地段就地起沙已发育有新月形沙丘及初期诸形态。发育时间短(约在1960年以后形成), 并且是演变再活跃的场所。下游下段(三角洲尾端以北)已全为流沙覆盖。仅从枯死胡抚和红柳稚丛分布反映过去柯床痕迹, 最远一支可延伸至古老的塔里木河。克里雅河下游现代沙漠化过程加剧的主要因素是中游人为活动。增大用水量。下游水量减少, 环境恶化, 而不是大沙漠前移所造成的。听以, 改善下游天蛛绿洲生态环境时, 中游应分配合理水量给下游, 以保持下游干三角洲中天然绿洲生态平衡。下游保存完整的天然绿洲建议作为国家级自然保护区。

Study on Formation and Development of Aeolian Landform and Trend of Environmental Change at Lower Reach of the Keriya River,Taklimakan Desert

The Keriya River is the second largest river stretching into Taklinakan Desert for 420 km, except Hetian River. Along with the trend of gradual decrease of discharge of the river downwards to lower reach, the geomorp-hological landscape along the river changes obviously from section to section. The Keriya River, after flowing out of the maintain pass, forms alluvial fan. its upper part is composed of gravel alluvium, middle part a farming oasis composed of silt and sandy loam, lower part composed of saline soils At lower course of Yeying, these two tributaries form two dry deltas respectively. On the eastern dry delta, river system is distributed in fan-shaped, the riverbed density reaches 4-8 km/km², there are intermittent rivers reached here and desert woodlands-Populus diversifolia and Tamarix spp.distributed along the river rings, covering an area of 210 km², where a few residential area distributed on it. As islands of sea, the complex sand dune chains were dissected by running water, forming isolated distribution of complex sand dunes on it. On the western dry delta, the dry riverbed on fan-shaped river system is intermittently distributed. It is completely a less-populated area with huge megadunes, longitudinal dune chains, eroded shrub sand mounds and withered Populus euphratica occurred on the riverbed. There are some ruins of ancient towns distributed discontinously on the river bank of the western tributary, which reflects that once there existed human activities in the historical period. Wind is the leading agent of the change of aeolian landforrn along the Keriya River course and the running water causes a great impact on regional variance of aeolian landform in extremely arid desert zone. The flooded riverring at the upper section of the lower reach of the Keriya River(from Daheyaa to Hetian) was affected by intermittent water and vegetated with reeds without development of mobile dunes. The first terrace of the upper flooded riverbed, is generally 1.5-3m high from riverbed and interspersed with Tamarix shrub, Populus euphratica woodlands. On sparsely wooded terraces, barchans, sanddune chains and shrub vegetated sand mounds have been formed by blown sands in situ. The second terrace, 8-9 m above the riverbed, is mainly tamarix vegetated area. Under the influence of the surrounding shifting sand encroachment and the reactivation of the fixed sand dunes after the vegetation being destroyed, the alternated landscape of barchans, sand dune chains and shurb vegetated sand mounds were formed. The third terrace, is completely covered with barchans, sand dune chains. The lower reach of the Keriya River,(northern section of Daheyan) refers to the dry delta on the fan-shaped plain, the water system of the Keriya River is scatterd in a fan-shaped way, forming a natural oasis with better water condition, the most remarkable characteristics of the aeolian landform on the dry delta lie in the complex sand dunes were intercepted into isolated ones by Populus euphratica trees and tamarix spp. shrubs. The barchans and embryonic forms have developed on the high dried riverbed under wind force, and developing in a certain period(formed since 1960). The lower section of lower reach of the Keriya River(northern end of dry delta) was completely covered with moving sand dunes. The traces of the past river can be reflected by the tortuous whithered Populus euphratica and tamarix spp. vegetated sand mounds, the furthest one reaches to the ancient Tarim River. In the lower reach of the Keriya River, the key factor leading to intensify the desertification process, is misuse of water at the middle reach and impacts of human activities which caused the environmental degradation, the encroachment of mobile dune is not considered as the main factor. Therefore, in consideration of the problem of preventing the environment of natural oases at lower reaches from being degraded, rationally distributing reasonable amount of water to the dry delta to keep equilibrium of ecobalance the river course is the best way to control desertification process.The natural oases at the lower reach of the Keriya River should be preserved as one of national park in desert. In addition, effort should be made(mainly in completing the existing protection system in the interior of oases, protecting the existing natural vegetation on the periphery of oasis) to maintain the stability and development of oases.